How can I tell my close friends I need to focus on myself?

I need to work on myself and i don’t know if my friends will understand that. we talk almost everyday on the phone and it’s draining because i need to focus on my education and my life. but talking to them on the phone and texting takes up my whole day and i don’t know how to approach it to them.
How can I tell my close friends I need to focus on myself?
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